1. Field of the Invention
The subject matter of the invention is a fast-processing photographic recording material for medical radiography, which stands out for its fast processability and high sensitivity while also displaying very good photographic and physical properties.
2. Description of Related Art
Medical radiography makes use of photographic recording materials (called X-ray films below) having at least one radiation-sensitive silver halide emulsion layer on both sides of a carrier in combination with intensifying screens. The physical and photographic properties of these X-ray films determine their suitability in terms of allowing the radiologist to make a reliable diagnosis of diseases. In order to reduce radiation exposure for patients as well as hospital personnel, there is a need for X-ray films which are as sensitive as possible. In addition to the uniform high quality requirements made of today's X-ray films, the fast availability of the image developed from them is also a significant aspect, for example, pictures which are taken during operations and which are needed to provide information on the further course of the surgery. Moreover, in hospitals or large physicians' practices it is often the case that pictures from several imaging devices, for example, X-ray machines, laser cameras, devices for monitoring photography, and copiers for X-ray films, are processed in the same film processor. This is why there is a desire for the highest possible throughput rate for the photographic films and thus the shortest possible processing times--less than 60 seconds--for X-ray films as well as for other photographic films, in film processors in such hospitals and physicians' practices.
The processing time of a photographic film depends primarily on the composition of the film in question, on the structure and on the mode of operation of the particular film processor, as well as on the developer solution and the fixing bath used in the film processor. All of the parameters--for example, the dryer geometry and drying time of the film processor or the absorption of process water by the particular photographic film--which influence the drying of the photographic films in the film processor are of special importance in this context.
The processing time is defined here as the time that an X-ray film in the standard format having edge lengths of 0.35 meter.times.0.35 meter needs to pass through a film processor, starting when the X-ray film is pulled in and ending with the complete release of the developed X-ray picture. This period of time may also be referred to as the "nose to drop" in the technical literature.
A photographic silver halide recording material is said to be fast-processing if it can be processed in a film processor within 30 to 60 seconds.
U.S. Pat. No. 4,897,340 describes an example of a roll processor as well as a formulation for a developer used in it as well as a fixing bath suitable for this processing.
In order to reduce the processing time of photographic films, U.S. Statutory Invention Registration No. H874 proposes the reduction of the total gelatin coating weight to a range from 2.2 to 3.1 g/m.sup.3 per side. However, this has a detrimental effect on certain properties of X-ray films such as, for example, sensitivity to wet pressure marks and scratches, graininess, pressure desensitization and sensitization as well as the image quality of the image made with this material.
As another way to shorten the processing time of X-ray films, it has been suggested to reduce the swelling of the binder by means of greater cross-linking. This measure, however, has a detrimental effect on the photographic properties such as gradation and maximum optical density.
A simultaneous reduction of binder and silver halide application in the recording material leads to a greater print through and thus to worse sharpness of the picture made with this material. This can only be unsatisfactorily compensated for by using filter dyes, since they cannot be completely washed out and thus they have a negative impact on the picture coloration of the X-ray picture made in this manner.
Another way to quickly process X-ray films proposed by U.S. Pat. No. 4,797,353 is to use polymers such as polyacrylamide and/or saccharose which can be washed out during the development process in the silver halide or protective layer.
However, the washable polymers contaminate the processor liquids and are thus disadvantageous. Moreover, such films with a low weight ratio of non-washable binder to silver have poor wet pressure properties.
Until now, no photographic recording material has been found for medical radiology that can be processed within 60 seconds with a film processor, while also displaying an adequately high sensitivity, good physical and photographic properties as well as high image quality.
The photographic recording materials which have been proposed so far for medical radiology and which can be processed within 60 seconds also yield differing sensitometric data as a function of the processing time. This is not desirable in actual practice since different exposure parameters are needed for different processing speeds.